Chemical cleaners are a significant portion of the industrial cleaning market. A chemical cleaner is typically aqueous and comprises an organic solvent to solubilize various soils, a surfactant which serves as a wetting agent, and a builder which serves to chelate ions present in water, such as magnesium and calcium. The types and ratios of these ingredients can vary considerably depending on the types of soils to be cleaned and the performance desired. It is common that all components are water soluble. In some instances, however, particularly with the solvent ingredient, the water solubility can be negligible. In these cases, components commonly called "couplers" or "hydrotropes" are used to increase the apparent water solubility of the organic solvent in the cleaning composition. The amount of coupler required depends on the type of coupler, organic solvent, and the other components of the mixture. It is typically preferred to use the minimum amount of coupler necessary to completely solubilize the solvent, as this tends to reduce the cost of the cleaning composition.
For example, U.S. Pat. No. 5,080,831 (VanEenam), describe an aqueous cleaner which includes at least one sparingly water soluble organic solvent having water solubility of about 0.2 weight percent to about 6 weight percent, a solubilizing additive and water. The solubilizing additive is present in an amount to render the sparingly water soluble organic solvent to just completely water soluble so that the resulting aqueous solution is a true solution (i.e., a clear mixture exhibiting no Tyndall effect) rather than an emulsion or microemulsion.
An aqueous composition that is formulated as a microemulsion is described in U.S. Pat. No. 5,158,710 (VanEenam). The microemulsion includes at least one sparingly water soluble organic solvent having water solubility of about 0.2 weight percent to about 6 weight percent, a builder, a solubilizing additive, and water. In this composition, the solubilizing additive is present in an amount that does not substantially exceed the amount required to transform the combination of the organic solvent and the builder from a true macroemulsion to a microemulsion but less than the amount required to transform the microemulsion to a true solution, wherein the microemulsion is clear and exhibits a Tyndall effect.
An aqueous degreaser composition is described in U.S. Pat. No. 5,419,848 (VanEenam). The composition includes at least one sparingly water soluble organic solvent having water solubility of about 0.2 weight percent to about 6 weight percent, a viscosifying thickener, and water. A stable emulsion having a viscosity of at least about 500 centipoise and a droplet size of about 0.1 to 3 millimicrons is produced after subjecting the composition to energetic mixing and/or shear conditions. This relatively thick composition is typically used in lotions, creams, emollients, lubricants, humectants and skin conditioners that do not defat the skin.